Grande Dixence SA marked a historic milestone on October 20, 2023, with the official inauguration of the fully refurbished Fionnay and Nendaz power stations and the penstock connecting the Lac des Dix reservoir to the Rhone plain. 

Grande Dixence, which has been a cornerstone of Switzerland's electricity generation for nearly six decades, underwent a comprehensive renovation over a six-year period, gradually resuming operations at the beginning of the year. 

The project involved a significant overhaul and upkeep of the entire downhill conduit connecting Lac des Dix to the Rhône plain. Grande Dixence SA, along with its shareholders, has allocated a substantial investment of CHF 240 million. Michael Wider, Chairman of the Board of Directors of Grande Dixence SA, underscores the importance of this endeavor, stating, "In order to uphold our commitment to safeguarding the nation's electricity supply for the foreseeable future, it was our duty to invest in the preservation of the power generation infrastructure handed down to us by our predecessors."

The initial phase involved a comprehensive analysis of the various components comprising the downhill route, leading to the identification of necessary renewal, repair, and restoration initiatives. This was subdivided into 89 distinct sub-projects and spanned from 2016 to 2023. According to Beat Imboden, Director of Grande Dixence SA, "Through the extensive efforts undertaken, Grande Dixence continues to fulfill its critical role as a foundational asset capable of swiftly injecting substantial power into the electricity grid, thereby upholding the crucial equilibrium between electricity supply and demand."

Each of the six generating units at Grande Dixence's two power stations, Fionnay and Nendaz, has undergone a comprehensive retrofit, including the installation of new valves, turbines, alternators, automatic control systems, and auxiliary services. The simultaneous execution of various sub-projects demanded meticulous coordination, necessitating the implementation of innovative solutions to meet ambitious deadlines. This was particularly evident during the phases when the facilities were being brought back into service, even before the entirety of the work was completed.

Commencing from the start of 2023, the generating units have been systematically reintegrated into operation, ensuring their contribution to Switzerland's electricity supply, especially during the crucial winter period. Both plants are anticipated to be fully operational once more by the conclusion of the winter season in 2023-2024.

The penstock, connecting Lac des Dix to the Rhône through the Fionnay and Nendaz power stations, has undergone a comprehensive overhaul. Specifically, the overhead segment of the penstock, spanning 850 meters between Péroua and Condémines, has been completely replaced, while the anti-corrosion protection of the subterranean portions has been renewed.

Additionally, the seven main valves along the downhill line have been subject to refurbishment. The safety valves at Louvie and Péroua, situated at the inception of the penstocks, have been substituted, and substantial renovation work has been performed on the valves at the entry points of the water supply galleries at the Grande Dixence dam and the Fionnay reservoir. Given the substantial size of these valves, measuring three meters in diameter, both the disassembly and installation procedures, as well as the logistical aspects, posed considerable challenges, further compounded by the remote, high-altitude locations of these sites.

The entire downhill line was reopened at the beginning of September 2022, enabling water to be supplied to the generating plants.

A distinctive aspect of the Grande Dixence complex is the presence of a secondary conduit connecting Lac des Dix to the Rhône lowlands. This channel directs water to the Bieudron power station, which stands as Switzerland's most formidable hydroelectric facility, boasting an impressive capacity of 1,200 MW. Notably, during the renovation process, all the water stored in the Grande Dixence dam remained available for harnessing, thereby fueling the turbines at the Bieudron plant.